Doctor of Philosophy

dissertationFollowing the progress of shrinking down the sizes of integrated circuit elements, optical lithography, which is the state of the art of patterning ever-small structures, has now almost reached its final limit. This limit to the size of the smallest feature that can be patterned using photolithography is imposed by the diffraction limit of light, generally accepted to be about half the wavelength of illumination. Absorbance Modulation Optical Lithography (AMOL) is a technique of super-resolution maskless photolithography with the potential to localize light to sub-diffraction limited spaces. AMOL uses a unique family of organic molecules called photochromes that can switch between two isomeric states based on the wavelength of photon that the states absorbs, a long wavelength photon (of wavelength λ2) and a short wavelength photon (of wavelength λ1). When a thin layer of this photochromic molecule, is subjected to simultaneous illumination by a focal spot at λ1 and a ring-shaped spot at λ2, it is rendered opaque everywhere except at very close to the center of the optical node in the ring shaped λ2 spot. This competing behavior of the absorbance of the layer to the two wavelengths and the state transitions allows only λ1 photons to penetrate through the λ2 node, creating a nanoscale illumination spot, the dimensions of which are far below the diffraction limit. A recording medium placed under this layer, such as photoresist can record this illumination. In this thesis, the development of AMOL as a cost effective super-resolution photolithography process is addressed. Firstly, an improvement to the AMOL process is affected by the removal of a barrier layer that was present in previous demonstrations in between the AML and the photoresist. Secondly, experimental verification of the AMOL feature-scaling trend is presented. Next, a comprehensive model to simulate the AMOL process is constructed using finite element method based full electromagnetic wave solutions. A couple of methods to realize AMOL patterning at very low light intensity levels are also demonstrated with both simulation and experimental verifications. Lastly, an optical system is described that is capable of extending the AMOL process to patterning aperiodic arbitrary features

Broadband lightweight flat lenses for longwave-infrared imaging

We experimentally demonstrate imaging in the longwave-infrared (LWIR) spectral band (8um to 12um) using a single polymer flat lens based upon multi-level diffractive optics. The device thickness is only 10{\mu}m, and chromatic aberrations are corrected over the entire LWIR band with one surface. Due to the drastic reduction in device thickness, we are able to utilize polymers with absorption in the LWIR, allowing for inexpensive manufacturing via imprint lithography. The weight of our lens is less than 100 times those of comparable refractive lenses. We fabricated and characterized two different flat lenses. Even with about 25% absorption losses, experiments show that our flat polymer lenses obtain good imaging with field of view of ~35degrees and angular resolution less than 0.013 degrees. The flat lenses were characterized with two different commercial LWIR image sensors. Finally, we show that by using lossless, higher-refractive-index materials like silicon, focusing efficiencies in excess of 70% can be achieved over the entire LWIR band. Our results firmly establish the potential for lightweight, ultra-thin, broadband lenses for high-quality imaging in the LWIR band